1. Field of the Invention
The present invention relates to a converting device for allowing an unused optical fiber in an optical cable to be utilized as a communication line when connection, laying, maintenance, etc. of an optical communication line such as an optical cable are performed.
2. Description of the Related Art
When connection, laying, maintenance, etc. of an optical cable for optical communication are performed, a person at an optical cable connection point (hereinafter referred to as a connection point) and a person in a terminal office, or persons at a plurality of connection points, must be in contact with each other. Conventionally, they stay in contact by using transceiver or telephones utilizing, for example, an intervening metal line or unused optical fiber within the optical cable, especially in a place where radio waves cannot be received/transmitted, such as a tunnel or the like. When the optical cable is of non-metal structure, i.e. one which does not include a twist pair, an unused optical fiber within the optical cable can be utilized for calls. Using a optical talk set, a call signal can be supplied to the optical fiber, thus enabling calls to be made (talking set using end to end optical fiber).
However, in order to connect the optical talk set to the optical fiber, it is necessary to extract a junction of the optical fiber from the housing in which the junction is enclosed. The optical fiber is then cut, and the sheath near the cut portions is removed. After a call is finished, the cut portions are reconnected to each other, and the junction is placed back in the housing to restore the optical fiber to its normal state. These operations, performed before and after a call, are troublesome and time-consuming.
In light of the above, the inventors first devised a clop on calling method for enabling calls to be made without the need to cut the optical fiber. According to this method, a piezoelectric element is provided on the transmission side of the optical fiber in which polarized light is transmitted. Using the piezoelectric element, vibration is externally applied to the optical fiber, thus modulating the plane of the polarized wave of the polarized light. On the receiving side of the optical fiber, a light signal whose the plane of the polarized wave has been modulated is extracted by local detection, thus enabling normal calls to be made. Thus, using this method, operations such as cutting the optical fiber and reconnecting the cut portions are unnecessary, since the piezoelectric element needs only to be placed in pressure contact with the optical fiber after the junction of the optical fiber is extracted from the housing.
However, like the previous method, the above method also entails an operation of extracting the junction of the optical fiber from the housing. Since it is hermetically sealed by a sealing member in order to prevent the housing from inundating with water, it is quite difficult to open the housing. While opening the housing is unavoidable in the case of work involving a connecting operation, such as when the optical cable is moved from one place to another or when a branch line of the cable is formed, opening the housing merely for the purpose of making a call is not practical.